I tried EPUBReader on 2016-02-03. Most things work except for one piece of crucial functionality: adding an epub file to your collection. That's kind of a deal-breaker.

If it's not a deal-breaker for you, then you can add the books in Firefox, then copy the epub directory from your Firefox profile to your Conkeror profile. I tested this and it works fine.

It may be possible to manually extract the epub to the epub directory and add the appropriate information to epub.sqlite but that probably won't be easy.

To navigate to your collection use "about:epubcatalog" and to view a specific book use "about:epubreader?id=1"